UB-9 was a little under 28 metres (92 ft) in length and displaced between 127 and 141 tonnes (125 and 139 long tons), depending on whether surfaced or submerged.

Sources do not report any more commanding officers assigned through the end of the war, so it's not clear if the submarine remained in commission.

At the end of the war, UB-9 was deemed unseaworthy and unable to surrender at Harwich with the rest of Germany's U-boat fleet.

After the German Army's rapid advance along the North Sea coast in the earliest stages of World War I, the German Imperial Navy found itself without suitable submarines that could be operated in the narrow and shallow seas off Flanders.

[4][Note 2] UB-9 was the first of the initial allotment of seven submarines—numbered up to UB-15—ordered on 15 October from AG Weser of Bremen, just shy of two months after planning for the class began.

Like all boats of the class, UB-9 was rated to a diving depth of 50 metres (160 ft), and could completely submerge in 33 seconds.